Automated assembly and mounting of solar cells on space panels

ABSTRACT

The present disclosure provides methods of fabricating a multijunction solar cell panel in which one or more of the steps are performed using an automated process. In some embodiments, the automated process uses machine vision.

This application is a continuation of U.S. patent application Ser. No.15/658,756 filed Jul. 25, 2017, which in turn is a continuation of U.S.patent application Ser. No. 15/170,269, filed Jun. 1, 2016, now U.S.Pat. No. 9,748,432.

The present application is also related to U.S. patent application Ser.No. 14/592,519, filed Jan. 8, 2015, and Ser. No. 14/719,111, filed May21, 2015.

All of the above applications are herein incorporated by reference intheir entireties.

BACKGROUND OF THE DISCLOSURE 1. Field of the Disclosure

The present disclosure relates to the field of photovoltaic solararrays, and more particularly to fabrication processes utilizing, forexample, multijunction solar cells based on III-V semiconductorcompounds fabricated into interconnected Cell-Interconnect-Cover Glass(CIC) assemblies and mounted on a support or substrate using automatedprocesses.

2. Description of the Related Art

Solar power from photovoltaic cells, also called solar cells, has beenpredominantly provided by silicon semiconductor technology. In the pastseveral years, however, high-volume manufacturing of III-V compoundsemiconductor multijunction solar cells for space applications hasaccelerated the development of such technology not only for use in spacebut also for terrestrial solar power applications. Compared to silicon,III-V compound semiconductor multijunction devices have greater energyconversion efficiencies and generally more radiation resistance,although they tend to be more complex to manufacture. Typical commercialIII-V compound semiconductor multijunction solar cells have energyefficiencies that exceed 27% under one sun, air mass 0 (AMO),illumination, whereas even the most efficient silicon technologiesgenerally reach only about 18% efficiency under comparable conditions.Under high solar concentration (e.g., 500×), commercially availableIII-V compound semiconductor multijunction solar cells in terrestrialapplications (at AM1.5D) have energy efficiencies that exceed 37%. Thehigher conversion efficiency of III-V compound semiconductor solar cellscompared to silicon solar cells is in part based on the ability toachieve spectral splitting of the incident radiation through the use ofa plurality of photovoltaic regions with different band gap energies,and accumulating the current from each of the regions.

In satellite and other space related applications, the size, mass andcost of a satellite power system are dependent on the power and energyconversion efficiency of the solar cells used. Putting it another way,the size of the payload and the availability of on-board services areproportional to the amount of power provided. Thus, as payloads becomemore sophisticated, the power-to-weight ratio of a solar cell becomesincreasingly more important, and there is increasing interest in lighterweight, “thin film” type solar cells having both high efficiency and lowmass.

Space applications frequently use high efficiency solar cells, includingmultijunction solar cells based on III-V compound semiconductors.Typical III-V compound semiconductor solar cells are fabricated on asemiconductor wafer in vertical, multijunction structures. Theindividual solar cells or wafers are then disposed in horizontal arrays,with the individual solar cells connected together in an electricalseries and/or parallel circuit. The shape and structure of an array, aswell as the number of cells it contains, are determined in part by thedesired output voltage and current.

Conventional space solar array panels at present are most oftencomprised of a relatively densely packed arrangement of large solarcells formed from group III-V compound semiconductor devices mounted ona rigid supporting panel and operating without lenses for opticalconcentration of sunlight. A conventional space solar array panel mayinclude a support, space solar cells disposed on the support,interconnection components for connecting the solar cells, and bypassdiodes also connected to the solar cells.

Solar panels are generally formed by combining a large number of solarcells in an array. Individual solar cells, frequently with a rectangularor generally square-shape and sometimes with cropped corners, areconnected in series to form a string of solar cells, whereby the numberof solar cells used in the string determines the output voltage. Solarcells or strings of solar cells can also be interconnected in parallel,so as to increase the output current. In the field of spaceapplications, individual solar cells are provided with interconnects andcover glass so as to form so-called CICs (Cell-Interconnect-Cover Glass)assemblies, which are then combined to form an array. Conventionally,these large solar cells have been mounted on a support andinterconnected using a substantial amount of manual labor. For example,first individual CICs are produced with each interconnect individuallywelded to each cell, and each cover glass individually mounted. Then,these CICs are connected in series to form strings, generally in asubstantially manual manner, including welding or soldering steps. Then,these strings are applied to a panel or substrate and interconnected, ina process that includes the application of adhesive, wiring, and otherassembly steps.

Close packing of the large solar cells on the space solar array panel ischallenging due to requirement for interconnection of the solar cells toform a series circuit and to implement and interconnect the bypassdiodes. An additional challenge can sometimes reside in the need tointerconnect a plurality of strings of series connected solar cells inparallel. All of this has traditionally been carried out in a manual andsubstantially labor-intensive manner.

There is a continuing need for improved methods of manufacturing andassembling photovoltaic solar arrays that can result in decreases incost and/or increases in performance.

SUMMARY OF THE DISCLOSURE

1. Objects of the Disclosure

It is an object of the present disclosure to provide an automatedprocess for producing solar cell panels for space applications.

It is another object of the present disclosure to provide an automatedassembly tool for producing solar cell panels for space applications.

It is an object of the disclosure to provide a supply cassette includinga plurality of solar cell assemblies connected in series that can beused in an automated process to form a solar array panel byautomatically placing and adhering said solar cell assemblies to thesupport.

It is another object of the disclosure to provide a method for making asolar cell panel.

It is another object of the disclosure to provide for an assemblystructure and method that facilitates automation of at least certainsteps of the process for manufacture of solar cell assemblies or CICsand panels of interconnected CICs.

Some implementations of the present disclosure may incorporate orimplement fewer of the aspects and features noted in the foregoingobjects.

2. Features of the Disclosure

Briefly, and in general terms, the present disclosure provides a methodof fabricating a solar cell panel in an automated process. For example,disclosed herein is a method of fabricating a multijunction solar cellarray panel comprising one or more of the steps of: fabricating a waferutilizing a metal organic chemical vapor deposition (MOCVD) reactor;metallizing the backside of the wafer; lithographically patterning anddepositing metal of the front side of the wafer; forming a mesa on thefront side of the wafer by lithography and etching; depositing anantireflective coating (ARC) over the wafer; dicing one or more solarcells from the wafer; testing the functionality of the one or more solarcells; attaching interconnects to the one of more solar cells; attachinga cover glass to each solar cell to form a Cell-Interconnect-Cover Glass(CIC); forming a string configuration of CICs; interconnecting stringconfigurations of CICs; bonding string configurations or interconnectedstring configurations to a substrate; configuring and wiring a panelcircuit; configuring a blocking diode; wiring a first terminal and asecond terminal of first and second polarities, respectively, for thesolar cell panel; and testing the functionality of the solar cell panel;wherein at least one of the method steps is performed using an automatedprocess.

In certain embodiments, the solar cells are III-V compound semiconductormultijunction solar cells, and fabricating the wafer comprises:providing a metal organic chemical vapor deposition (MOCVD) systemconfigured to independently control the flow of source gases forgallium, indium aluminum, and arsenic; selecting a reaction time andtemperature and a flow rate for each source gas to form thecontinuously-graded interlayer disposed on the bottom subcell, whereinthe source gas for indium is trimethylindium (InMe₃), the sources gasfor gallium in trimethylgallium (GaMe₃), the source gas for arsenic isarsine (AsH₃), and the source gas for aluminum is trimethylaluminum(Al₂Me₆).

In other certain embodiments, fabricating a wafer comprises: providing afirst substrate; depositing on the first substrate a sequence of layersof semiconductor material forming at least first, second, and thirdsolar cells; forming a grading interlayer on said first, second, and/orsaid third solar cell; depositing on said grading interlayer a secondsequence of layers of semiconductor material forming a fourth solarcell, the fourth solar cell lattice mismatched to the third solar cell;mounting and boding a surrogate substrate on top of the sequence oflayers; and removing the first substrate, wherein forming the gradeditnterlayer comprises: picking an interlayer composed of InGaAlAs; usinga computer program to identify a set of compositions of the formula(In_(x)Ga_(1-x))_(y)Al_(1-y)As defined by specific values of x and y,wherein 0<x<1 and 0<y<1, each composition having a constant bandgap;identifying a lattice constant for one side of the graded interlayerthat matches the middle subcell and a lattice constant for an opposingside of the interlayer that matches the bottom subcell; and identifyinga subset of compositions of the formula (In_(x)Ga_(1-x))_(y)Al_(1-y)Ashaving the constant bandgap that are defined by specific values of x andy, wherein 0<x<1 and 0<y<1, and wherein the subset of compositions havelattice constants ranging from the identified lattice constant thatmatches the adjacent subcell to the identified lattice constant thatmatches the bottom subcell.

In another embodiment, the present disclosure provides a method offabricating a multijunction solar cell array on a carrier using one ormore automated processes, the method comprising: providing a firstmultijunction solar cell including a first contact pad and a secondcontact pad disposed adjacent the top surface of the multijunction solarcell along a first peripheral edge thereof; attaching a first electricalinterconnect to the first contact pad of said first multijunction solarcell; attaching a second electrical interconnect to the second contactpad of the first multijunction solar cell; positioning said firstmultijunction solar cell over an adhesive region of a permanent carrierusing an automated machine/vision apparatus; mounting a cover glass oversaid first multijunction solar cell; and bonding said firstmultijunction solar cell to said adhesive region using pressure and/orheat.

In some embodiments of the disclosure, the support is a KAPTON® layer,that is, a polymide film layer. KAPTON® is a trademark of E.I. du Pontde Nemours and Company. The chemical name for KAPTON® is poly(4,4′-oxydiphenylene-pyromellitimide). Other polymide film sheets orlayers may also be used.

In some embodiments, the support has a thickness of between 25 and 100microns, or between 1 mil (25.4 μm) and 4 mil (101.6 μm).

In some embodiments, the support has a thickness of between 10 and 25microns.

In some embodiments, a metal layer is attached to the support layer inan adhesive-less manner, to limit outgassing when used in a spaceenvironment.

In some embodiments the support is mounted on a metallic honeycombstructure.

The substrate may be a rigid substrate, such as an aluminum honeycombsubstrate with carbon composite face sheet, or it may be a flexiblesubstrate, such as a polymide film.

In some embodiments, after making the bonding connection, at least twosolar cell devices are automatically interconnected using a pick andplace process for positioning the interconnectors, followed by automaticparallel gap welding.

In some embodiments, contact pads are established by an automaticmetallic plating process.

In some embodiments the at least two solar cell devices areautomatically electrically connected, for example wire bonded together,with the at least two solar cell devices having co-planar front-sideelectrical contacts.

In another aspect, the present disclosure provides a space vehicle andits method of fabrication comprising: a payload disposed on or withinthe space vehicle; and a power source for the payload, including anarray of solar cell assemblies mounted on a panel, with at least onesolar cell panel or solar cell assembly being of the type describedherein.

Some implementations of the present disclosure may incorporate orimplement fewer of the aspects and features noted in the foregoingsummaries.

Additional aspects, advantages, and novel features of the presentdisclosure will become apparent to those skilled in the art from thisdisclosure, including the following detailed description as well as bypractice of the disclosure. While the disclosure is described below withreference to preferred embodiments, it should be understood that thedisclosure is not limited thereto. Those of ordinary skill in the arthaving access to the teachings herein will recognize additionalapplications, modifications and embodiments in other fields, which arewithin the scope of the disclosure as disclosed and claimed herein andwith respect to which the disclosure could be of utility.

BRIEF DESCRIPTION OF THE DRAWING

To complete the description and in order to provide for a betterunderstanding of the disclosure, a set of drawings is provided. Saiddrawings form an integral part of the description and illustrateembodiments of the disclosure, which should not be interpreted asrestricting the scope of the disclosure, but just as examples of how thedisclosure can be carried out. The drawings comprise the followingfigures:

FIG. 1A is a top plan view of a wafer with two solar cells beingimplemented;

FIG. 1B is a top plan view of a wafer with a single solar cell beingimplemented;

FIG. 2A is a top plan view of a portion of a solar cell according to thepresent disclosure;

FIG. 2B is a cross-sectional view of a multijunction solar cell throughthe 2B-2B plane of the solar cell of FIG. 2A;

FIG. 2C is a cross-sectional view of the solar cell of FIG. 2A throughthe 2C-2C plane shown in FIG. 2A;

FIG. 2D is a top plan view of a portion of a solar cell with croppedcorners and interconnect elements;

FIG. 2E is a perspective view of a portion of a solar cell with croppedcorners of FIG. 2A more specifically depicting the interconnectelements;

FIG. 2F is a cross-sectional view of the solar cell of FIG. 2A throughthe 2C-2C plane shown in FIG. 2A after connection of an interconnectelement;

FIG. 2G is a top plan view of the solar cell of FIG. 2A after attachmentof a cover glass thereby forming a Cell-Interconnect-Cover Glass (CIC);

FIG. 2H is a cross-sectional view of the Cell-Interconnect-Cover Glass(CIC) of FIG. 2G through the 2H-2H plane shown in FIG. 2A;

FIG. 2I is a cross-sectional view of a portion of the solar cell of FIG.2A that has been interconnected to an adjacent solar cell using theinterconnect element depicted in FIG. 2F;

FIG. 3 is a flowchart representing a method in accordance with anembodiment of the present disclosure;

FIG. 4 is a perspective view of a metallic honeycomb structure which canbe used for mounting a support;

FIG. 5 is a cross-sectional view of an aluminum honeycomb substrate withcarbon composite face sheet; and

FIG. 6 is a cross-sectional view of an aluminum honeycomb substrate withcarbon composite face sheet and a co-cured polyimide substrate.

DESCRIPTION OF ILLUSTRATIVE EMBODIMENTS

Details of the present invention will now be described includingexemplary aspects and embodiments thereof. Referring to the drawings andthe following description, like reference numbers are used to identifylike or functionally similar elements, and are intended to illustratemajor features of exemplary embodiments in a highly simplifieddiagrammatic manner. Moreover, the drawings are not intended to depictevery feature of the actual embodiment nor the relative dimensions ofthe depicted elements, and are not drawn to scale.

A variety of different features of multijunction solar cells aredisclosed in the related applications noted above. Some, many, or all ofsuch features may be included in the structures and processes associatedwith the solar cells of the present disclosure. However, moreparticularly, the present disclosure is directed to several embodimentsof the interconnect element.

More generally, however, the present disclosure may be adapted tomultijunction solar cells as disclosed in related applications that mayinclude three, four, five, or six subcells, with band gaps in the rangeof 1.8 to 2.2 eV (or higher) for the top subcell; 1.3 to 1.8 eV and 0.9to 1.2 eV for the middle subcells; and 0.6 to 0.8 eV for the bottomsubcell.

The present disclosure provides an apparatus and methods to automatemany of the processes and material handling steps associated with thefabrication and assembly of a covered-interconnect-cell or “CIC” usingmultijunction solar cells, and the mounting of such CICs on a solarpanel or support. More specifically, the present disclosure intends toprovide a relatively simple and reproducible technique that is suitablefor use in a high volume production environment in which varioussemiconductor layers are deposited in an MOCVD reactor, and subsequentprocessing steps are defined and selected to minimize any physicaldamage to solar cell and the quality of the semiconductor devices,thereby ensuring a relatively high yield of operable solar cells meetingspecifications at the conclusion of the fabrication processes.

FIG. 1A is a top plan view of a wafer with two solar cells (cell 1 andcell 2) being implemented.

FIG. 1B is a top plan view of a wafer with a single solar cell (cell 3)being implemented.

FIG. 2A is a top plan view of a portion of a solar cell 900 according tothe present disclosure depicting metal grid layers 940 and metal contactpad 952 adjacent peripheral edge regions 950 and 951 of solar cell 900.

FIG. 2B is a cross-sectional view of a multijunction solar cell throughthe 2B-2B plane of the solar cell of FIG. 2A which may be used as anexample in which the processes as provided by the present disclosure maybe implemented. In FIG. 2B, each dashed line indicates the active regionjunction between a base layer and emitter layer of a subcell.

As shown in the illustrated example of FIG. 2B, the bottom subcell 901includes a substrate 912 formed of p-type germanium (“Ge”) which alsoserves as a base layer. A contact pad 911 can be formed on the bottom ofbase layer 912 to provide electrical contact to the multijunction solarcell 303. The bottom subcell 901 further includes, for example, a highlydoped n-type Ge emitter layer 914, and an n-type indium gallium arsenide(“InGaAs”) nucleation layer 916. The nucleation layer is deposited overthe base layer 912, and the emitter layer is formed in the substrate bydiffusion of deposits into the Ge substrate, thereby forming the n-typeGe layer 914. Heavily doped p-type aluminum gallium arsenide (“AlGaAs”)and heavily doped n-type gallium arsenide (“GaAs”) tunneling junctionlayers 918, 917 may be deposited over the nucleation layer 916 toprovide a low resistance pathway between the bottom and middle subcells.

In the illustrated example of FIG. 2B, the middle subcell 902 includes ahighly doped p-type aluminum gallium arsenide (“AlGaAs”) back surfacefield (“BSF”) layer 920, a p-type InGaAs base layer 922, a highly dopedn-type indium gallium phosphide (“InGaP₂”) emitter layer 924 and ahighly doped n-type indium aluminum phosphide (“AlInP₂”) window layer926. The InGaAs base layer 922 of the middle subcell 902 can include,for example, approximately 1.5% In. Other compositions may be used aswell. The base layer 922 is formed over the BSF layer 920 after the BSFlayer is deposited over the tunneling junction layers 918 of the bottomsubcell 901.

The BSF layer 920 is provided to reduce the recombination loss in themiddle subcell 902. The BSF layer 920 drives minority carriers from ahighly doped region near the back surface to minimize the effect ofrecombination loss. Thus, the BSF layer 920 reduces recombination lossat the backside of the solar cell and thereby reduces recombination atthe base layer/BSF layer interface. The window layer 926 is deposited onthe emitter layer 924 of the middle subcell 902. The window layer 926 inthe middle subcell 902 also helps reduce the recombination loss andimproves passivation of the cell surface of the underlying junctions.Before depositing the layers of the top cell 903, heavily doped n-typeInGaP and p-type AlGaAs tunneling junction layers 927, 928 may bedeposited over the middle subcell 902.

In the illustrated example, the top subcell 909 includes a highly dopedp-type indium gallium aluminum phosphide (“InGaAlP”) BSF layer 930, ap-type InGaP₂ base layer 932, a highly doped n-type InGaP₂ emitter layer934 and a highly doped n-type InAlP₂ window layer 936. The base layer932 of the top subcell 903 is deposited over the BSF layer 930 after theBSF layer 930 is formed over the tunneling junction layers 928 of themiddle subcell 902. The window layer 936 is deposited over the emitterlayer 934 of the top subcell after the emitter layer 934 is formed overthe base layer 932. A cap or contact layer 938 may be deposited andpatterned into separate contact regions over the window layer 936 of thetop subcell 903. The cap or contact layer 938 serves as an electricalcontact from the top subcell 903 to metal grid layer 940. The doped capor contact layer 938 can be a semiconductor layer such as, for example,a GaAs or InGaAs layer.

After the cap or contact layer 938 is deposited, the grid lines 940 areformed. The grid lines 940 are deposited via evaporation andlithographically patterned and deposited over the cap or contact layer938. The mask is subsequently lifted off to form the finished metal gridlines 940 as depicted in FIG. 2B, and the portion of the cap layer thathas not been metallized is removed, exposing the surface of the windowlayer 936.

In some embodiments, a trench or channel 971 shown in FIG. 2C, orportion of the semiconductor structure, is also etched around each ofthe solar cells. These channels 971 define a peripheral boundary betweenthe solar cell (later to be scribed from the wafer) and the rest of thewafer, and leaves a mesa structure (or a plurality of mesas, in the caseof more than one solar cell per wafer) which define and constitute thesolar cells later to be scribed and diced from the wafer.

As more fully described in U.S. Patent Application Publication No.2010/0012175 A1 (Varghese et al.), hereby incorporated by reference inits entirety, the grid lines 940 are preferably composed of Ti/Au/Ag/Au,although other suitable materials may be used as well.

During the formation of the metal contact layer 940 deposited over thep+ semiconductor contact layer 938, and during subsequent processingsteps, the semiconductor body and its associated metal layers and bondedstructures will go through various heating and cooling processes, whichmay put stress on the surface of the semiconductor body. Accordingly, itis desirable to closely match the coefficient of thermal expansion ofthe associated layers or structures to that of the semiconductor body,while still maintaining appropriate electrical conductivity andstructural properties of the layers or structures. Thus, in someembodiments, the metal contact layer 940 is selected to have acoefficient of thermal expansion (CTE) substantially similar to that ofthe adjacent semiconductor material. In relative terms, the CTE may bewithin a range of 0 to 15 ppm per degree Kelvin different from that ofthe adjacent semiconductor material. In the case of the specificsemiconductor materials described above, in absolute terms, a suitablecoefficient of thermal expansion of layer 940 would range from 5 to 7ppm per degree Kelvin. A variety of metallic compositions and multilayerstructures including the element molybdenum would satisfy such criteria.In some embodiments, the layer 940 would preferably include the sequenceof metal layers Ti/Au/Mo/Ag/Au, Ti/Au/Mo/Ag, or Ti/Mo/Ag, where thethickness ratios of each layer in the sequence are adjusted to minimizethe CTE mismatch to GaAs. Other suitable sequences and materialcompositions may be used in lieu of those disclosed above.

In some embodiments, the metal contact scheme chosen is one that has aplanar interface with the semiconductor, after heat treatment toactivate the ohmic contact. This is done so that (i) a dielectric layerseparating the metal from the semiconductor doesn't have to be depositedand selectively etched in the metal contact areas; and (ii) the contactlayer is specularly reflective over the wavelength range of interest.

The grid lines are used as a mask to etch down the surface to the windowlayer 936 using a citric acid/peroxide etching mixture.

An antireflective (ARC) dielectric coating layer 942 is applied over theentire surface of the “top” side of the wafer with the grid lines 940.

FIG. 2C is a highly simplified cross-sectional view of the solar cell ofFIG. 2A similar to that of FIG. 2B, but in a view longitudinally along agrid line. The cross-sectional view of the solar cell of FIG. 2A isthrough the 2C-2C plane. A contact pad 952 electrically connected to thegrid line metal 940 is depicted.

FIG. 2D is a top plan view of a portion of a solar cell 900 with croppedcorners 991 and 992 near a peripheral edge 990 of solar cell 900. FIG.2D also depicts interconnect elements 962 and 972, and metal grid layers940.

FIG. 2E is a perspective view of a portion of a solar cell 900 withcropped corners of FIG. 2A more specifically depicting the interconnectelement 962 having members 315 and 316 connected to metal contact pad952. FIG. 2E also depicts metal grid layers 940 of solar cell 900.

FIG. 2F depicts the attachment of an interconnection member 960 to themetal contact pad 952. The interconnection member 960 is a planarrectangular clip having a first flat end-portion 961 welded to the metalcontact 952, a second portion 962 connected to the first end-portion 961and extending above the surface of the solar cell, and a third portion963 connected to the second portion 962 and being serpentine in shape,and flat second end-portion 964 extending below the bottom of the solarcell and designed and oriented so that its flat upper side surface maybe welded to the bottom metal contact 911 of an adjacent solar cell 800as shown in FIG. 2I.

FIG. 2G is a top plan view of the solar cell of FIG. 2A after attachmentof a cover glass 981 to the top of solar cell 900, thereby forming aCell-Interconnect-Cover Glass (CIC). FIG. 2G also depicts interconnectelements 962 and 972.

FIG. 2H is a cross-sectional view of the solar cell of FIG. 2F after thenext process step of attachment of a cover glass 981 to the top of thesolar cell by an adhesive 980. The cover glass 981 is typically about 4mils thick. Although the use of a cover glass is desirable for manyenvironmental conditions and applications, it is not necessary for allimplementations, and additional layers or structures may also beutilized for providing additional support or environmental protection tothe solar cell.

FIG. 2I is a cross-sectional view of the solar cell of FIG. 2H, which isnow designated as cell 300, after the next process step of alignmentwith the edge of an adjacent similar solar cell 800, in the process offabricating an interconnected array or string of solar cells. Thesimilar solar cell 800 includes layers 811, 812 through 836, 838, and840 similar to layers 911, 912, . . . through 936, 938, and 940respectively of solar cell 300. A cover glass 881 is attached byadhesive 880 to the solar cell 800 similar to that in solar cell 300.

FIG. 3 is a flowchart representing a method in accordance with anembodiment of the present disclosure. Certain embodiments of theinvention can include one or more of the method steps of waferfabrication (101), backside metallization (102), front side lithographyand metal deposition (103), mesa lithography and etch (104),antireflective coating (ARC) deposition (105), cell dicing from thewafer (106), cell testing (107), attaching interconnects and configuringand attaching bypass diodes (108), attaching cover glass to form CIC(109), forming string configuration (110), forming stringinterconnection (111), CIC string bonding to substrate (112), panelcircuit configuration and wiring (113), blocking diode configuration(114), terminal wiring (115), and functional testing (116).

In certain embodiments of the present disclosure, one or more of theabove-recited method steps may be performed using an automated process.Exemplary automated processes for some of the steps are furtherdiscussed herein below. However, the present disclosure is intended toinclude alternative automated processes that are known in the art foreach method step. Further, the exemplary automated processes discussedherein to carry out one method step may be used to carry out othermethod steps not explicitly discussed herein. In some embodiments aplurality of recited method steps may be performed using one or moreautomated processes. In certain embodiments, all of the recited methodsteps may be performed using one or more automated processes.

In some embodiments, the automated process may use a robot (e.g., pickand place assembly tools) to perform a conventional manual process.

In some embodiments, a wire bonding laser welding machine can be usedfor attaching interconnects to one or more solar cells.

In some embodiments, the one or more automated processes may use machinevision. Machine vision can include imaging-based automatic inspectionand analysis for applications such as automatic inspection, processcontrol, and robot guidance. Although conventional (2D visible light)imaging is most commonly used in machine vision, alternatives includeimaging various infrared bands, line scan imaging, 3D imaging ofsurfaces, and X-ray imaging. The most commonly used method for 3Dimaging is scanning based triangulation which utilizes motion of theproduct or image during the imaging process. Other 3D methods used formachine vision are time of flight, grid based, and stereoscopic.

For machine vision, the imaging device (e.g. camera) can either beseparate from the main image processing unit or combined with it inwhich case the combination can be a smart camera or a smart sensor. Whenseparated, the connection may be made to specialized intermediatehardware such as a frame grabber using either a standardized or custominterface. Machine vision can also use digital cameras capable of directconnections (without a framegrabber) to a computer.

Although the vast majority of machine vision applications usetwo-dimensional imaging, machine vision applications utilizing 3Dimaging are a growing alternative. One method is grid array basedsystems using pseudorandom structured light system. Another method ofgenerating a 3D image is to use laser triangulation, where a laser isprojected onto the surfaces of an object and the deviation of the lineis used to calculate the shape. In machine vision this is accomplishedwith a scanning motion, either by moving the workpiece, or by moving thecamera and laser imaging system. Stereoscopic vision can be used inspecial cases involving unique features present in both views of a pairof cameras.

Solar cell wafers can be prepared by automated methods of depositingIII-V compound semiconductor layers and other layers (e.g.,antireflective coating. ARC) on a substrate to fabricate a wafer. Suchmethods that are readily amenable to automation include, for example,metal organic chemical vapor deposition (MOCVD) methods that are readilyknown in the art. Backside metallization of a cell can be performed, forexample, by evaporation or electrodeposition on a polyimide layer (e.g.,a KAPTON® layer).

Features such as grid lines and mesas can be formed on the front sidesof the wafers using conventional techniques such as lithography, metaldeposition, and etching techniques, all of which are readily amenable toautomation using, for example, machine vision.

Solar cell configurations particularly suitable for assembly usingautomated processes include those that are described in U.S. patentapplication Ser. No. 14/592,519, filed Jan. 8, 2015; Ser. No.14/719,911, filed May 21, 2015; 14/729,412, filed Jun. 3, 2015; and Ser.No. 14/729,422, filed Jun. 3, 2015, all of which are incorporated hereinby reference in their entireties.

One or more solar cells can be formed from a wafer using conventionaltechniques such as dicing or scribing. The size and shape of the solarcells can be varied as desired for particular applications as disclosed,for example, in U.S. patent application Ser. No. 14/592,519, filed Jan.8, 2015, which is incorporated herein by reference in its entirety.Dicing or scribing of solar cells from a wafer is particularly amenableto automation using machine vision.

The functionality of the one or more solar cells can be tested byconventional automated testing equipment.

Interconnects can be attached to the one of more solar cells using, forexample, automatic soldering or laser welding equipment.

In some embodiments, one end of the interconnects can have parallel gapapertures, and the interconnects can be connected, for example, byapplying a parallel gap welding tool.

In some embodiments, all electrical components in the solar cell arraycan be continuously encapsulated with CV grade silicone, which can beused to mount multi-cell large area coverglass, or as a surface forapplying advanced coatings such as Cover Glass Replacement (CGR) orradiation resistant coatings. This approach can produce an array that iselectrically isolated, can mitigate high voltage arcing problems, caneliminate cracks and seams to minimize the need for expensive inter-cellgrouting, and can enable electrostatic cleanliness.

Dispensing of silicone onto solar cells and coverglass has typicallybeen performed using a patterned silk screening process or squeegeeapproaches. These processes require additional materials and processassociated with designing and producing templates, as well as thewasteful nature of hand mixing and application. These processes areinherently wasteful and laborious, driving high cost and low processthroughput. The approach described herein provides for the simple lowcost and high precision application of silicone adhesive to solar cellassemblies with standardized carriers.

In some embodiments, a silicone can be dispensed on the solar cellusing, for example, an automated Asymtek machine with visual recognitionfor maximum precision.

A cover glass can be attached to each solar cell to form aCell-Interconnect-Cover Glass (CIC) using automated methods. Forexample, in some embodiments the CIC assembly process can be completedwith the implementation of automated assembly and lamination. Afterlarge area or precision dispensing operations have been performed, atemporary carrier can be fixtured in a component placement machine.Using computerized visual recognition of fiducial location points, anumerically controlled component placement machine can pick the largearea solar cell coverglass from a cartridge stack, placing this upon theuncured silicone dispensed in the previous step, which can then be curedto form the CIC.

In some embodiments, a similar component placement step can beimplemented to both load a wire-bonding machine, as well as to performthe final submodule placement onto any suitable number of solar arraysubstrates such as a flexible membrane or a rigid composite sandwichpanel. Such automated methods can reduce or eliminate labor intensivehand operations from the entire process.

CICs can be positioned and placed on a support in an automated manner,for example, by a pick and place assembly tool to form a stringconfiguration of CICs as described, for example, in U.S. patentapplication Ser. No. 14/719,911, filed May 21, 2015, and Ser. No.14/729,412, filed Jun. 3, 2015, both of which are incorporated herein byreference in their entireties. Bypass and blocking diodes can beconfigured by similar methods.

Solar cell in a string can be interconnected using, for example,standard automation equipment for wire bonding such as an automatedthermosonic wire-bonding machine, and also as disclosed, for example, inU.S. patent application Ser. No. 14/719,911, filed May 21, 2015, whichis incorporated herein by reference in its entirety.

String configurations or interconnected string configurations of solarcells positioned and placed on a support in an automated manner, forexample, by a pick and place assembly tool as described, for example, inU.S. patent application Ser. No. 14/719,911, filed May 21, 2015, andSer. No. 14/729,412, filed Jun. 3, 2015, both of which are incorporatedherein by reference in their entireties. In certain embodiments, thestring configurations or interconnected string configurations of solarcells can be bonded to the substrate by the automatic application ofpressure and/or heat and interconnected in a similar manner as discussedherein above.

Configuring and wiring a panel circuit and terminal can be performedusing conventional automated wiring equipment.

Testing the functionality of the solar cell panel can be performed byautomated methods similar to those discussed herein above for testing ofindividual solar cells. For example, 5-cell submodules have beenfabricated using the processes described herein. Testing on thesubmodules performed included electrical continuity, grounding, andisolation testing. The submodules were subjected them to thermal cyclingfrom −120° C. to +120° C. to represent typical LEO orbital conditions;from −180° C. to +80° C. to represent typical GEO orbital conditions;and in a related program, to plasma environments at high voltage, as aninitial qualification to Low Earth Orbit environments. All tests showedgood performance and reliability for the solar cell strings before andafter exposure to these environments.

An engineering economic analysis of the benefits of the automatedbonding and assembly processes was performed to quantify the benefits tolowering the cost of solar cell strings sub-modular building blocks. Thedata in Table 1 demonstrates substantial array integration costreduction. The results, summarized in Table 1, are on a comparativebasis only and do not necessarily represent a particular absolute pricefor a photovoltaic array or panel in a particular quantity. Laborestimates were made based on fully burdened labor rates including apostulated overhead, but do not account for potential alternativemanufacturing cell and team structures. Labor rates also do not accountfor the lower skill level labor that could be implemented with automatedassembly equipment compared to the higher level of skill that is oftenrequired for manual fixtured or semi-automated assembly.

TABLE 1 Cost Projections for Automated vs. Traditional Approach Material& Process Cost Traditional Integration $/Watt Material Cell 250.00Interconnect Foil 20.73 Individual Coverglass 5.12 Adhesive 3.70 Diode12.50 Wire 1.00 Consumables, Templated, Ect. 3.00 Total Materials 296.05Integration Process Skilled Technician Premium   25% Weld Interconnectto Cell 6 Weld Interconnect Cell to Cell 6 Individual Silicone 7Individual Cover Glass 8 Mask and Dispense Silicone 12 Transfer Tool 5Tilting Sheet 5 Laydown 8 Bag and Cure 8 Cleanup 18 Panel Wiring 12Solder 5 Grouting 25 Documentation and Inspection 35 Total Labor $/Watt160 Yield 85.0% Integrated Cost $/Watt 537 THINS Automated Integration$/Watt Material Cell 250.00 Gold Wire 0.48 Large Area Coverglass 6.11Adhesive 1.55 Diode 12.50 Terminal Strip 12.72 Flex Harness 1.96 TotalMaterials 285.32 Integration Process Skilled Technician Premium   0%Pick & Place Cell, Diode, Terminal Strips 4 Automated Wire BondInterconnect 3 Automated Encapsulation 4 Apply Cover Glass or CGR 3Automated Dispense Silicone 3 Automated Pick and Place Sub-module 3Vacuuum Bag Press Cure 3 Cleanup (precision dispense net process) 0Automated Solder Placement 5 Solder Oven Re-flow 3 Grouting (multi-cellglass needs less) 10 Documentation and Inspection 15 Total Labor $/Watt56 Yield 97.5% Integrated Cost $/Watt 350 *costs are relative, burdenedat an assumed overhead rate, and do not account for productionquantities, and the potentially lower skill level needed for automatedequipment operation.

FIG. 4 is a perspective view of a metallic honeycomb structure 200 whichcan be used for mounting a support.

FIG. 5 is a cross-sectional view of an aluminum honeycomb substrate 200with carbon composite face sheet 201 attached thereto. In someembodiments, a double sided adhesive film can be positioned on the topsurface of the face sheet, and the bottom surface of the adhesive filmcan be bonded to the top surface of the face sheet by, for example,co-curing. In some embodiments, a plurality of layers of carboncomposite sheets can be embedded in a matrix of cyanate ester adhesive.The polyimide can then be put on top and the whole stack co-cured.

In some embodiments, a sequence of solar cell assemblies can bepositioned over the top surface of the adhesive film, and each of thesequence of solar cell assemblies can be sequentially bonded to apredefined region on the top surface of the adhesive film, for example,by automatic application of pressure and/or heat. In some embodiments,the predefined region contains a pressure sensitive adhesive, and noadhesive is present on other regions of the top surface of the facesheet.

FIG. 6 is a cross-sectional view of an aluminum honeycomb substrate 200with carbon composite face sheet 201 attached to aluminum honeycombsubstrate 200, and co-cured polyimide substrate 202 attached to carboncomposite face sheet 201.

It is to be noted that the terms “front”, “back”, “top”, “bottom”,“over”, “on”, “under”, and the like in the description and in theclaims, if any, are used for descriptive purposes and not necessarilyfor describing permanent relative positions. It is understood that theterms so used are interchangeable under appropriate circumstances suchthat the embodiments of the disclosure described herein are, forexample, capable of operation in other orientations than thoseillustrated or otherwise described herein.

Furthermore, those skilled in the art will recognize that boundariesbetween the above described operations are merely illustrative. Themultiple units/operations may be combined into a single unit/operation,a single unit/operation may be distributed in additionalunits/operations, and units/operations may be operated at leastpartially overlapping in time. Moreover, alternative embodiments mayinclude multiple instances of a particular unit/operation, and the orderof operations may be altered in various other embodiments.

In the claims, the word ‘comprising’ or ‘having’ does not exclude thepresence of other elements or steps than those listed in a claims. Theterms “a” or “an”, as used herein, are defined as one or more than one.Also, the use of introductory phrases such as “at least one” and “one ormore” in the claims should not be construed to imply that theintroduction of another claim element by the indefinite articles “a” or“an” limits any particular claim containing such introduced claimelement to disclosures containing only one such element, even when theclaim includes the introductory phrases “one or more” or “at least one”and indefinite articles such as “a” or “an”. The same holds true for theuse of definite articles. Unless stated otherwise, terms such as “first”and “second” are used to arbitrarily distinguish between the elementssuch terms describe. Thus, these terms are not necessarily intended toindicate temporal or other prioritization of such elements. The factthat certain measures are recited in mutually different claims does notindicate that a combination of these measures cannot be used toadvantage.

The present disclosure can be embodied in various ways. The abovedescribed orders of the steps for the methods are only intended to beillustrative, and the steps of the methods of the present disclosure arenot limited to the above specifically described orders unless otherwisespecifically stated. Note that the embodiments of the present disclosurecan be freely combined with each other without departing from the spiritand scope of the disclosure.

Although some specific embodiments of the present disclosure have beendemonstrated in detail with examples, it should be understood by aperson skilled in the art that the above examples are only intended tobe illustrative but not to limit the scope of the present disclosure. Itshould be understood that the above embodiments can be modified withoutdeparting from the scope and spirit of the present disclosure which areto be defined by the attached claims.

What is claimed is:
 1. A method of fabricating a solar cell array panelcomprising one or more of the steps of: providing a substrate; providinga plurality of multijunction solar cells; positioning and mounting acover glass over each discrete respective multijunction solar cell toform a discrete Cell-Interconnect-Cover Glass (CIC) assembly;positioning and attaching a plurality of discrete CIC assemblies to thesubstrate; electrically connecting the plurality of multijunction solarcells in electrical series to provide a solar cell string; and testing afunctionality of an assembled solar cell panel; wherein at least one ofthe method steps is performed using one or more automated processes; andwherein at least one of the one or more automated processes uses machinevision.
 2. The method of claim 1, wherein at least one of the one ormore automated processes uses a robot.
 3. The method of claim 1 whereinat least one of the one or more automated processes uses a pick andplace assembly tool; a wire bonding machine or a laser welding machinefor attaching interconnects to one or more solar cells; automatic vapordeposition equipment; automated metal plating equipment; automatedlithographic techniques; automatic etching techniques; automatic testingequipment; automatic soldering or laser welding equipment; automaticdispensing equipment; automated wiring equipment; and/or automaticapplication of pressure and/or heat.
 4. The method of claim 1, whereinthe substrate is flexible and is composed of a poly(4,4′-oxydiphenylene-pyromellitimide) material.
 5. The method of claim1, further comprising attaching a blocking diode to the substrate andelectrically connecting it in series with the solar cell string and abus bar disposed on the substrate.
 6. The method of claim 1, furthercomprising providing a first terminal and a second terminal of first andsecond polarities, respectively, connected to the circuit of stringconfigurations on the solar cell panel.
 7. The method of claim 1,wherein each multijunction solar cell includes a first contact terminalof a first conductivity type, and a second contact terminal of a secondconductivity type, each contact terminal being disposed adjacent to thetop surface of the multijunction solar cell along a peripheral edgethereof; welding a first electrical interconnect to the first contactterminal; and welding a second electrical interconnect to the secondcontact terminal.
 8. The method of claim 1, further comprisingpositioning each CIC assembly over an adhesive region of the substrate;and bonding said each multijunction solar cell to the adhesive regionusing pressure and/or heat.
 9. A method of fabricating a solar cellarray panel comprising one or more of the steps of: providing asubstrate; positioning and attaching a plurality of solar cells to thesubstrate; electrically connecting the plurality of solar cells inseries to provide a solar cell string; and positioning and mounting acover glass over each discrete solar cell; and testing a solar cellarray panel to space qualification; wherein at least one of the methodsteps is performed using one or more automated processes; and wherein atleast one of the one or more automated processes uses a pick and placeassembly tool; a wire bonding machine or a laser welding machine forattaching interconnects to one or more solar cells; automatic vapordeposition equipment; automatic metal plating equipment; automaticlithographic techniques; automatic etching techniques; automatic testingequipment; automatic soldering or laser welding equipment; automaticdispensing equipment; automated wiring equipment; and/or automaticapplication of pressure and/or heat.
 10. The method of claim 9, whereinat least one of the one or more automated processes uses a robot. 11.The method of claim 9, further comprising testing a functionality of anassembled solar cell array panel.
 12. The method of claim 9, wherein thesubstrate is flexible and is composed of a poly(4,4′-oxydiphenylene-pyromellitimide) material.
 13. The method of claim9, further comprising attaching a blocking diode to the substrate andelectrically connecting it in series with the solar cell string and abus bar disposed on the substrate.
 14. The method of claim 9, furthercomprising providing a first terminal and a second terminal of first andsecond polarities, respectively, connected to a circuit of stringconfigurations on the solar cell array panel.
 15. The method of claim 9,wherein each solar cell includes a first contact terminal of a firstconductivity type, and a second contact terminal of a secondconductivity type, each contact terminal being disposed adjacent to thetop surface of the solar cell along a peripheral edge thereof; welding afirst electrical interconnect to the first contact terminal; and weldinga second electrical interconnect to the second contact terminal.
 16. Themethod of claim 9, further comprising positioning each solar cell overan adhesive region of the substrate; and bonding said each solar cell tothe adhesive region using pressure and/or heat.
 17. The method of claim9, wherein the solar cells are multijunction solar cells.
 18. The methodof claim 9, further comprising mounting the substrate on a metallichoneycomb structure.
 19. The method of claim 18, further comprisingproviding a carbon composite face sheet over the metallic honeycombstructure.
 20. A method of fabricating a solar array panel comprisingone or more of the steps of: providing a substrate; providing aplurality of multijunction solar cells; positioning and mounting a coverglass over each respective multijunction solar cell to form a discreteCell-Interconnect-Cover Glass (CIC) assembly; providing a discreteelectrical interconnect having a first end and a second end; welding thefirst end of the interconnect to a terminal of a first conductivity typeon a first multijunction solar cell and the second end of theinterconnect to a terminal of a second conductivity type on secondmultijunction solar cell disposed adjacent to the first multijunctionsolar cell; and wherein at least one of the method steps is performedusing one or more automated processes; and wherein at least one of theone or more automated processes uses machine vision.